Ground water is used as raw water for tap water and in industries requiring a large amount of water, such as food industry, soft drink, brewing, public baths, and dyeing industry. Meanwhile, currently, iron and manganese components contained in ground water are a major problem. Iron and manganese are components necessary for human body. However, iron or manganese exceeding certain amounts give water a metallic taste or cause red or black water. Such water is not only suitable for drinking but causes various problems in these industries. In addition, in construction work, extraction of ground water is an essential process. However, when the ground water contains large amounts of iron and manganese, discarding the ground water directly in sewage system is prohibited by law, and there is a problem in that the ground water must be discarded after removing iron and manganese contained in the ground water.
Currently, the most widely used apparatuses for removing iron and manganese add an oxidizing agent such as sodium hypochlorite or a flocculant such as polyaluminium chloride (PAC) into the raw water to oxidize iron and manganese dissolved in water so as to produce insoluble iron oxide and manganese oxide and then filter away the oxides through filter sand.
However, the water treatment apparatuses by method of adding an oxidizing agent or a flocculant consume a relatively large amount of the oxidizing agent or flocculant, thus increasing cost for these agents. In addition, since sodium hypochlorite used as the oxidizing agent remains in the post-treatment cleaning water even after the oxidation of iron and manganese, it produces trihalomethane, which is a carcinogen. Accordingly, in order to remove the substance, filtering of the water through an activated carbon layer is further needed, which is uneconomical. If the installation of the activated carbon layer is deferred due to economic considerations, it is necessary to analyze and monitor, constantly, water after filtering to adjust the amount of an oxidizing agent added according to the situation, in order to prevent the production of trihalomethane due to an excessive addition of the oxidizing agent. This is disadvantageous in terms of increasing maintenance and operation cost in addition to purchase cost for the chemical agent. Additionally, the water treatment apparatuses by method of adding a chemical agent include an aeration tank, a flocculation tank, a precipitation tank, a sand filter tower, an iron and manganese removing tower, and a chemical agent tank, where system is complicated and the entire apparatus is large-scaled, thus necessitating a wide installation space. Accordingly, there is a problem in that such apparatuses cannot be installed in environments where space is limited, such as city areas. Furthermore, in the water treatment apparatuses by method of adding a chemical agent, treatment of wastewater after cleaning is necessary. However, in that case, since the sand contains the chemical agent, the wastewater must be treated as an industrial waste, and there are inconveniences such as disposal site restrictions.
A water treatment apparatus disclosed in Patent Literature 1 has been proposed to remove the disadvantages of the conventional water treatment apparatuses adding a chemical agent and provide a water treatment apparatus that can remove iron, manganese, and other soluble components contained in ground water or the like by oxidation and insolubilization of these components using a simple and compact apparatus without using chemicals such as oxidizing agents and flocculants. In this water treatment apparatus, while jet nozzles turn raw water into a jet water stream, air is introduced into the jet nozzles through air inlets or air introducing pipes open to the insides of the jet nozzles. Then, jet streams including a large number of air bubbles from raw water ejection outlets of the nozzles are hit against the surface of water above a filter layer arranged below the ejection outlets to cause fierce aeration in the water and on the surface of a filter medium. This causes soluble components such as iron and manganese in the water to be oxidized and turned into insoluble components, which are then caught on the surface of filter medium particles such as filter sand forming the filter layer. Accordingly, without any use of chemicals such as oxidizing agents and flocculants, the simple and compact apparatus can achieve the insolubilization and filtering of iron, manganese, and other soluble components in raw water.
In addition, as another type of a water treatment apparatus for cleaning a surface layer of a water treatment apparatus, a rotary cleaning apparatus disclosed in Patent Literature 2 is known. In the rotary cleaning apparatus, water is ejected diagonally downward from a plurality of water ejecting nozzles provided in a longitudinal direction of a horizontal rotary pipe attached to a lower end of a vertical rotation shaft to hit against the surface of a filter layer so as to rotate the horizontal rotary pipe in response to the hitting, thereby stirring and cleaning the surface layer of the filter medium by the water ejected from each water ejecting nozzle.